1. Field of the Invention
The present invention relates to an electrophoretic display technique for changing visual condition by controlling electric field application in a display unit having charged particles and a section for applying voltage, especially a method for making an electrophoretic solution including two kinds of charged particles having different charging polarities.
2. Related Background of the Invention
As an electrophoretic display device, there is an electrophoretic display device using two kinds of particles wherein two kinds of dispersion particles having different colors and different charging polarities are dispersed in a colorless dispersion medium. JP-A-2003-295235 is an example of related art, wherein a technique that enables multicolor display by evolving such a two-particle electrophoretic display device is proposed.
As in the case of JP-A-2003-295235, there have been no particular considerations on the mixing ratio of the two kinds of particles. When the two kinds of particles have close physical properties, it is not relatively difficult to obtain preferable display performance by mixing the two in each sufficient quantity.
In many cases, however, there are significant differences between the sizes, weights, etc. of positively charged particles and negatively charged particles. Under such significant differences in physical properties, it has been difficult to find a proper quantity of particles to be included. For example, in order to calculate a preferable mixing ratio, it has been inevitable to repeat experiments many times by varying the quantity of particles to be mixed. It is fortunate if a preferable result is obtained accidentally in the first try. If not, there has been no way but to repeat experiments aimlessly. Under such circumstances, development has not progressed efficiently. Moreover, there has been almost no proof that the determined mixing ratio is the most preferable one.